Organic light emitting materials and devices

ABSTRACT

An organic light emitting device is provided. The device has an anode, a cathode, and an emissive layer disposed between the anode and the cathode, the emissive layer further comprising an emissive material having the structure:  
                 
 
     wherein each of the variables are defined herein.

REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims priority from U.S.Provisional Patent Application 60/404,213 filed Aug. 16, 2002 and is acontinuation-in-part of U.S. patent application Ser. 10,288,785 alsoentitled “Organic Light Emitting Materials and Devices”, each of whichis incorporated herein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention is directed to phosphorescence basedorganic light emitting materials and devices that have improvedelectroluminescent characteristics.

BACKGROUND

[0003] Opto-electronic devices that make use of organic materials arebecoming increasingly desirable for a number of reasons. Many of thematerials used to make such devices are relatively inexpensive.Consequently, organic opto-electronic devices have the potential forcost advantages over inorganic devices. In addition, the inherentproperties of organic materials, such as their flexibility, may makethem well suited for particular applications such as fabrication on aflexible substrate. Examples of organic opto-electronic devices includeorganic light emitting devices (OLEDs), organic phototransistors,organic photovoltaic cells, and organic photodetectors. For OLEDs, theorganic materials may have performance advantages over conventionalmaterials. For example, the wavelength at which an organic emissivelayer emits light may generally be readily tuned with appropriatedopants.

[0004] As used herein, the term “organic” includes polymeric materialsas well as small molecule organic materials that may be used tofabricate organic opto-electronic devices. “Small molecule” refers toany organic material that is not a polymer, and “small molecules” mayactually be quite large. Small molecules may include repeat units insome circumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be an fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

[0005] OLEDs make use of thin organic films that emit light when voltageis applied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

[0006] OLED devices are generally (but not always) intended to emitlight through at least one of the electrodes, and one or moretransparent electrodes may be useful in an organic opto-electronicdevice. For example, a transparent electrode material, such as indiumtin oxide (ITO), may be used as the bottom electrode. A transparent topelectrode, such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745,which are incorporated by reference in their entireties, may also beused. For a device intended to emit light only through the bottomelectrode, the top electrode does not need to be transparent, and may becomprised of a thick and reflective metal layer having a high electricalconductivity. Similarly, for a device intended to emit light onlythrough the top electrode, the bottom electrode may be opaque and/orreflective. Where an electrode does not need to be transparent, using athicker layer may provide better conductivity, and using a reflectiveelectrode may increase the amount of light emitted through the otherelectrode, by reflecting light back towards the transparent electrode.Fully transparent devices may also be fabricated, where both electrodesare transparent. Side emitting OLEDs may also be fabricated, and one orboth electrodes may be opaque or reflective in such devices.

[0007] As used herein, “top” means furthest away from the substrate,while “bottom” means closest to the substrate. For example, in a devicehaving two electrodes, the bottom electrode is the electrode closest tothe substrate, and is generally the first electrode fabricated. Thebottom electrode has two surfaces, a bottom surface closest to thesubstrate, and a top surface further away from the substrate. Where afirst layer is described as “disposed over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in physical contact with” the second layer. For example,a cathode may be described as “disposed over” an anode, even thoughthere are various organic layers in between.

[0008] The technology of organic light emitting diodes (OLEDs) isundergoing rapid development. OLEDs originally utilized theelectroluminescence produced from electrically excited molecules thatemitted light from their singlet states as disclosed, for example, inU.S. Pat. No. 4,769,292. Such radiative emission from a singlet excitedstate is referred to as fluorescence. More recent work has demonstratedthat higher power efficiency OLEDs can be made using molecules that emitlight from their triplet state, defined as phosphorescence. Suchelectrophosphorescence makes it possible for phosphorescent OLEDs tohave substantially higher quantum efficiencies than are possible forOLEDs that only produce fluorescence. This is based on the understandingthat the excitons created in an OLED are produced, according to simplestatistical arguments as well as experimental measurements,approximately 75% as triplet excitons and 25% as singlet excitons. Thetriplet excitons more readily transfer their energy to triplet excitedstates that can produce phosphorescence whereas the singlet excitonstypically transfer their energy to singlet excited states that canproduce fluorescence.

[0009] In contrast, only a small percentage (about 25%) of excitons influorescent devices are capable of producing the fluorescentluminescence that is obtained from a singlet excited state. Theremaining excitons in a fluorescent device, which are produced in thelowest triplet excited state of an organic molecule, are typically notcapable of being converted into the energetically unfavorable highersinglet excited states from which the fluorescence is produced. Thisenergy, thus, becomes lost to radiationless decay processes that heat-upthe device.

[0010] Since the discovery that phosphorescent materials could be usedin an OLED, Baldo et al., “Highly Efficient Phosphorescent Emission fromOrganic Electroluminescent Devices” Nature, vol. 395, 151-154, 1998,there is now much interest in finding more efficientelectrophosphorescent materials. OLEDs utilizing phosphorescentmaterials are disclosed, for example, in U.S. Pat. No. 6,303,238 whichis incorporated by reference in its entirety.

[0011] Typically, phosphorescent emission from organic molecules is lesscommon than fluorescent emission. However, phosphorescence can beobserved from organic molecules under an appropriate set of conditions.It would be desirable if more efficient electrophosphorescent materialscould be found, particularly materials that produce their emission inthe technologically useful blue and green colors of the visiblespectrum.

SUMMARY OF THE INVENTION

[0012] An organic light emitting device is provided. The device has ananode, a cathode, and an emissive layer disposed between the anode andthe cathode, the emissive layer further comprising an emissive materialhaving the structure:

[0013] wherein M is a heavy metal with an atomic weight of greater than40;

[0014] each of R₂ through R₅ and R′₃ through R′₆ are independentlyselected from the group consisting of H, halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, PO₃R, C≡CR, alkyl, alkenyl, aryl, heteroaryl, aryl orheteroaryl groups substituted with halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, orPO₃R, OR, SR, NR₂ (including cyclic-amino), PR₂ (includingcyclic-phosphino), where R is hydrogen, an alkyl group, an aryl group ora heteroaryl group;

[0015] at least one of R₃ and R₅ is either an electron withdrawing groupor an electron donating group;

[0016] m is at least 1, n is at least 0 and X—Y is an ancillary ligand.

[0017] In a preferred embodiment, R₃ is a substituent having a Hammettvalue less than about −0.17, between about −0.15 and 0.05, or greaterthan about 0.07.

[0018] In a further preferred embodiment, m is an integer from 1 to 4, nis an integer from 1 to 3; and,

[0019] is a monoanionic ligand, preferably a non carbon coordinatingligand.

[0020] Specific embodiments of the present invention are directed toOLEDs using emissive phosphorescent organometallic compounds thatproduce improved electrophosphorescence in the blue region of thevisible spectrum. The emissive material itself is also provided. Theemissive material may have improved stability, and may provide asaturated blue emission.

[0021] Another preferred embodiment of the present invention comprises adevice with an emissive material having the structure:

[0022] wherein M is a heavy metal with an atomic weight of greater thanor equal to 40; m is at least 1; n is at least 0; X—Y is an ancillaryligand; R₂ and R₄ are both F; R₃ is a substituent having a Hammett valueless than about −0.17, between about −0.15 and 0.05, or greater thanabout 0.07; and each of R₃, R₅ and R′₃ through R′₆ are independentlyselected from the group consisting of H, halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, PO₃R, C≡CR, alkyl, alkenyl, aryl, heteroaryl, aryl orheteroaryl groups substituted with halogens, CN, CF₃, C,F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, orPO₃R; OR, SR, NR₂ (including cyclic-amino), PR₂ (includingcyclic-phosphino), where R is hydrogen, an alkyl group, an aryl group ora heteroaryl group

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 shows an organic light emitting device having separateelectron transport, hole transport, and emissive layers, as well asother layers.

[0024]FIG. 2 shows an inverted organic light emitting device that doesnot have a separate electron transport layer.

[0025]FIG. 3 shows stability plots for various materials.

DETAILED DESCRIPTION

[0026] Generally, an OLED comprises at least one organic layer disposedbetween and electrically connected to an anode and a cathode. When acurrent is applied, the anode injects holes and the cathode injectselectrons into the organic layer(s). The injected holes and electronseach migrate toward the oppositely charged electrode. When an electronand hole localize on the same molecule, an “exciton,” which is alocalized electron-hole pair having an excited energy state, is formed.Light is emitted when the exciton relaxes via a photoemissive mechanism.In some cases, the exciton may be localized on an excimer or anexciplex. Non-radiative mechanisms, such as thermal relaxation, may alsooccur, but are generally considered undesirable.

[0027] The initial OLEDs used emissive molecules that emitted light fromtheir singlet states (“fluorescence”) as disclosed, for example, in U.S.Pat. No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

[0028] More recently, OLEDs having emissive materials that emit lightfrom triplet states (“phosphorescence”) have been demonstrated. Baldo etal., “Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151 154, 1998; (“BaldoI”) and Baldo et al., “Very high efficiency green organic light emittingdevices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75,No. 3, 4 6 (1999) (“Baldo II”), which are incorporated by reference intheir entireties. Phosphorescence may be referred to as a “forbidden”transition because the transition requires a change in spin states, andquantum mechanics indicates that such a transition is not favored. As aresult, phosphorescence generally occurs in a time frame exceeding atleast 10 nanoseconds, and typically greater than 100 nanoseconds. If thenatural radiative lifetime of phosphorescence is too long, triplets maydecay by a non-radiative mechanism, such that no light is emitted.Organic phosphorescence is also often observed in molecules containingheteroatoms with unshared pairs of electrons at very low temperatures.2,2′ bipyridine is such a molecule. Non-radiative decay mechanisms aretypically temperature dependent, such that a material that exhibitsphosphorescence at liquid nitrogen temperatures may not exhibitphosphorescence at room temperature. But, as demonstrated by Baldo, thisproblem may be addressed by selecting phosphorescent compounds that dophosphoresce at room temperature.

[0029] Generally, the excitons in an OLED are believed to be created ina ratio of about 3:1, i.e., approximately 75% triplets and 25% singlets.See, Adachi et al., “Nearly 100% Internal Phosphorescent Efficiency InAn Organic Light Emitting Device,” J. Appl. Phys., 90, 5048 (2001),which is incorporated by reference in its entirety. In many cases,singlet excitons may readily transfer their energy to triplet excitedstates via “intersystem crossing,” whereas triplet excitons may notreadily transfer their energy to singlet excited states. As a result,100% internal quantum efficiency is theoretically possible withphosphorescent OLEDs. In a fluorescent device, the energy of tripletexcitons is generally lost to radiationless decay processes that heat upthe device, resulting in much lower internal quantum efficiencies. OLEDsutilizing phosphorescent materials that emit from triplet excited statesare disclosed, for example, in U.S. Pat. No. 6,303,238, which isincorporated by reference in its entirety.

[0030] Phosphorescence may be preceded by a transition from a tripletexcited state to an intermediate non-triplet state from which theemissive decay occurs. For example, organic molecules coordinated tolanthanide elements often phosphoresce from excited states localized onthe lanthanide metal. However, such materials do not phosphorescedirectly from a triplet excited state but instead emit from an atomicexcited state centered on the lanthanide metal ion. The europiumdiketonate complexes illustrate one group of these types of species.

[0031] Phosphorescence from triplets can be enhanced over fluorescenceby confining, preferably through bonding, the organic molecule in closeproximity to an atom of high atomic number. This phenomenon, called theheavy atom effect, is created by a mechanism known as spin orbitcoupling. Such a phosphorescent transition may be observed from anexcited metal to ligand charge transfer (MLCT) state of anorganometallic molecule such as tris(2 phenylpyridine)iridium(III).Molecules that phosphoresce from MLCT triplet states, However, typicallyemit light that is of lower energy than that observed from the unboundorganic ligand. This lowering of emission energy presents a challenge inthe development of organic molecules that phosphoresce in thetechnologically useful blue and green colors of the visible spectrumwhere the unperturbed phosphorescence typically occurs.

[0032]FIG. 1 shows an organic light emitting device 100. The figures arenot necessarily drawn to scale. Device 100 may include a substrate 110,an anode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order.

[0033] Substrate 110 may be any suitable substrate that provides desiredstructural properties. Substrate 110 may be flexible or rigid. Substrate110 may be transparent, translucent or opaque. Plastic and glass areexamples of preferred rigid substrate materials. Plastic and metal foilsare examples of preferred flexible substrate materials. Substrate 110may be a semiconductor material in order to facilitate the fabricationof circuitry. For example, substrate 110 may be a silicon wafer uponwhich circuits are fabricated, capable of controlling OLEDs subsequentlydeposited on the substrate. Other substrates may be used. The materialand thickness of substrate 110 may be chosen to obtain desiredstructural and optical properties.

[0034] Anode 115 may be any suitable anode that is sufficientlyconductive to transport holes to the organic layers. The material ofanode 115 preferably has a work function higher than about 4 eV (a “highwork function material”). Preferred anode materials include conductivemetal oxides, such as indium tin oxide (ITO) and indium zinc oxide(IZO), aluminum zinc oxide (AlZnO), and metals. Anode 115 (and substrate110) may be sufficiently transparent to create a bottom-emitting device.A preferred transparent substrate and anode combination is commerciallyavailable ITO (anode) deposited on glass or plastic (substrate). Aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. Anode 115 may be opaque and/or reflective. A reflective anode115 may be preferred for some top-emitting devices, to increase theamount of light emitted from the top of the device. The material andthickness of anode 115 may be chosen to obtain desired conductive andoptical properties. Where anode 115 is transparent, there may be a rangeof thickness for a particular material that is thick enough to providethe desired conductivity, yet thin enough to provide the desired degreeof transparency. Other anode materials and structures may be used.

[0035] Hole transport layer 125 may include a material capable oftransporting holes. Hole transport occurs predominantly through thehighest occupied molecular orbit (HOMO) levels of the “charge carryingcomponent” the hole transporting layer This component may be the basematerial of the hole transport layer 125, or it may be a dopant. Holetransport layer 125 may be intrinsic (undoped), or doped. Doping may beused to enhance conductivity. α-NPD and TPD are examples of intrinsichole transport layers. An example of a p-doped hole transport layer ism-MTDATA doped with _(F4)-TCNQ at a molar ratio of 50:1, as disclosed inU.S. patent application Ser. No. 10/173,682 to Forrest et al., which isincorporated by reference in its entirety. Other hole transport layermaterials and structures may be used.

[0036] As disclosed herein, emissive layer 135 includes an organicmaterial capable of emitting photons of light when electrons drop from alowest unoccupied molecular orbital (LUMO) of layer 135 where theycombine with holes in the highest occupied molecular orbital of layer135. Accordingly, a current flow passed between anode 115 and cathode160 through emissive layer 135 can produce an emission of light. In apresent embodiment, emissive layer 135 comprises a phosphorescentemissive material such as those disclosed herein. Phosphorescentmaterials are preferred over fluorescent materials because of the higherluminescent efficiencies associated with such materials.

[0037] Emissive layer 135 may comprise a host material capable oftransporting electrons and/or holes, doped with an emissive materialthat may trap electrons, holes, and/or excitons, such that excitonsrelax from the emissive material via a photoemissive mechanism. Examplesof host materials include but are not limited to Alq₃, CBP and mCP.Alternatively, emissive layer 135 may comprise a single material thatcombines transport and emissive properties. Whether the emissivematerial is a dopant or a major constituent, emissive layer 135 mayinclude additional materials, such as dopants that tune the emission ofthe emissive material Emissive layer 135 may include a plurality ofemissive materials capable of, in combination, emitting a desiredspectrum of light. Emissive material may be included in emissive layer135 in a number of ways. For example, an emissive small molecule may beincorporated into a polymer. Examples of emissive and host materialsknown in the art are disclosed in U.S. Pat. No. 6,303,238 to Thompson etal., which is incorporated by reference in its entirety.

[0038] In a present embodiment, electron transport layer 140 maycomprise a material capable of transporting electrons. Electrontransport layer 140 may be intrinsic (undoped), or doped. Doping may beused to enhance conductivity. Alq3 is an example of an intrinsicelectron transport layer. An example of an n-doped electron transportlayer material is BPhen doped with Li at a molar ratio of 1:1, asdisclosed in U.S. patent application Ser. No. 10/173,682 to Forrest etal., which is incorporated by reference in its entirety. Other electrontransport layers materials and structures may be used. The chargecarrying component of the electron transport layer may be selected suchthat electrons can be efficiently injected from the cathode into theLUMO (Lowest Unoccupied Molecular Orbital) energy level of the electrontransport layer. Electron transport occurs predominantly through thelowest unoccupied molecular orbit (LUMO) levels of the “charge carryingcomponent” of the hole transporting layer. This component may be thebase material, or it may be a dopant. The LUMO level of an organicmaterial may be generally characterized by the electron affinity of thatmaterial while the relative electron injection efficiency of a cathodemay be generally characterized in terms of the work function of thecathode material. Accordingly, the preferred properties of an electrontransport layer and the adjacent cathode may be specified in terms ofthe electron affinity of the charge carrying component of the ETL andthe work function of the cathode material. In particular, so as toachieve high electron injection efficiency, the work function of thecathode material is preferably not greater than the electron affinity ofthe charge carrying component of the electron transport layer by morethan about 0.75 eV, more preferably, by not more than about 0.5 eV.Similar considerations apply to any layer into which electrons are beinginjected.

[0039] Cathode 160 may be any suitable material or combination ofmaterials known to the art, such that cathode 160 is capable ofconducting electrons and injecting them into the organic layers ofdevice 100. Cathode 160 may be transparent or opaque, and may bereflective. Metals and metal oxides are examples of suitable cathodematerials. Cathode 160 may be a single layer, or may have a compoundstructure. FIG. 1 shows a compound cathode 160 having a thin metal layer162 and a thicker conductive metal oxide layer 164. In a compoundcathode, preferred materials for the thicker layer 164 include ITO, IZO,and other materials known to the art. U.S. Pat. Nos. 5,703,436 and5,707,745, which are incorporated by reference in their entireties,disclose examples of cathodes including compound cathodes having a thinlayer of metal such as Mg:Ag with an overlying transparent,electrically-conductive, sputter-deposited ITO layer. The part ofcathode 160 that is in contact with the underlying organic layer,whether it is a single layer cathode 160, the thin metal layer 162 of acompound cathode, or some other part, is preferably made of a materialhaving a work function lower than about 4 eV (a “low work functionmaterial”). Other cathode materials and structures may be used.

[0040] Blocking layers may be used to reduce the number of chargecarriers (electrons or holes) and/or excitons that leave the emissivelayer. An electron blocking layer 130 may be disposed between emissivelayer 135 and the hole transport layer 125, to block electrons fromleaving emissive layer 135 in the direction of hole transport layer 125.Similarly, a hole blocking layer 140 may be disposed between emissivelayer 135 and electron transport layer 145, to block holes from leavingemissive layer 135 in the direction of electron transport layer 140.Blocking layers may also be used to block excitons from diffusing out ofthe emissive layer.

[0041] The theory and use of blocking layers is described in more detailin U.S. Pat. No. 6,097,147 and U.S. patent application Ser. No.10/173,682 to Forrest et al., which are incorporated by reference intheir entireties. The conventional “blocking layer” is generallybelieved to reduce the number of charge carriers and/or excitons thatleave the emissive layer by presenting an energy barrier that the chargecarrier or exciton has difficulty surmounting. For example, holetransport is generally thought to be related to the Highest OccupiedMolecular Orbital (HOMO) of an organic semiconductor. A “hole blocking”material may therefore be generally characterized as a material that hasa HOMO energy level significantly less than that of the material fromwhich the holes are being blocked. A first HOMO energy level isconsidered “less than” a second HOMO energy level if it is lower on aconventional energy level diagram, which means that the first HOMOenergy level would have a value that is more negative than the secondHOMO energy level. For example, through the density function theory(DFT) calculation (B3LYP 6-31G*) using the Spartan 02 software package,Ir(ppy)₃ has a HOMO energy level of −4.85 eV. BCP has a HOMO energylevel of −5.87 eV, which is 1.02 eV less than that of Ir(ppy)₃, makingit an excellent hole blocker. ZrQ₄ has a HOMO energy level of −5.00,only 0.15 eV less than that of Ir(ppy)₃, such that little or no holeblocking is expected. mer-GaQ₃ has a HOMO energy level of −4.63 eV,which is greater than that of Ir(ppy)₃, such that no hole blocking atall is expected.

[0042] If the emissive layer includes different materials with differentenergy levels, the effectiveness of these various materials as holeblocking layers may be different, because it is the difference in HOMOenergy levels between the blocking layer and the blocked layer that issignificant, not the absolute HOMO energy level. The absolute HOMOlevel, however, may be useful in determining whether a compound will bea good hole blocker for particular emissive layers. For example, amaterial having a HOMO energy level of about −5.15 eV or less may beconsidered a reasonable hole blocking material for Ir(ppy)3, which is arepresentative emissive material. Generally, a layer having a HOMOenergy level that is at least 0.25 eV less than that of an adjacentlayer may be considered as having some hole blocking properties. Anenergy level difference of at least 0.3 eV is preferred, and an energylevel difference of at least 0.7 eV is more preferred. Similarly, theenergy of an exciton is generally believed to be related to the band gapof a material. An “exciton blocking” material may generally be thoughtof as a material having a band gap significantly larger than thematerial from which excitons are being blocked. For example, a materialhaving a band gap that is about 0.1 eV or more larger than that of anadjacent material may be considered a good exciton blocking material.

[0043] Generally, injection layers are comprised of a material that mayimprove the injection of charge carriers from one layer, such as anelectrode or an organic layer, into an adjacent organic layer. Injectionlayers may also perform a charge transport function. In device 100, holeinjection layer 120 may be any layer that improves the injection ofholes from anode 115 into hole transport layer 125. CuPc is an exampleof a material that may be used as a hole injection layer from an ITOanode 115, and other anodes. In device 100, electron injection layer 150may be any layer that improves the injection of electrons into electrontransport layer 145. LiF/Al is an example of a material that may be usedas an electron injection layer into an electron transport layer from anadjacent layer. Other materials or combinations of materials may be usedfor injection layers. Depending upon the configuration of a particulardevice, injection layers may be disposed at locations different thanthose shown in device 100. More examples of injection layers areprovided in U.S. patent application Ser. No. 09/931,948 to Lu et al.,which is incorporated by reference in its entirety. A hole injectionlayer may comprise a solution deposited material, such as a spin-coatedpolymer, e.g., PEDOT:PSS, or it may be a vapor deposited small moleculematerial, e.g., CuPc or MTDATA.

[0044] A hole injection layer (HIL) may planarize or wet the anodesurface so as to provide efficient hole injection from the anode intothe hole injecting material. A hole injection layer may also have acharge carrying component having HOMO (Highest Occupied MolecularOrbital) energy levels that favorably match up, as defined by theirrelative ionization potential (IP) energies, with the adjacent anodelayer on one side of the HIL and the hole transporting layer on theopposite side of the HIL. Using a doped HIL allows the dopant to beselected for its electrical properties, and the host to be selected formorphological properties such as wetting, flexibility, toughness, etc.Preferred properties for the HIL material are such that holes can beefficiently injected from the anode into the HIL material. Inparticular, the charge carrying component of the HIL preferably has anIP not more than about 0.7 eV greater that the IP of the anode material.More preferably, the charge carrying component has an IP not more thanabout 0.5 eV greater than the anode material. Similar considerationsapply to any layer into which holes are being injected. HIL materialsare distinguished from conventional hole transporting materials that aretypically used in the hole transporting layer of an OLED in that suchHIL materials may have a hole conductivity that is substantially lessthan the hole conductivity of conventional hole transporting materials.The thickness of the HIL of the present invention may be thick enough tohelp planarize or wet the surface of the anode layer. For example, anHIL thickness of as little as 10 nm may be acceptable for a very smoothanode surface. However, since anode surfaces tend to be very rough, athickness for the HIL of up to 50 nm may be desired in some cases.

[0045] A protective layer may be used to protect underlying layersduring subsequent fabrication processes. For example, the processes usedto fabricate metal or metal oxide top electrodes may damage organiclayers, and a protective layer may be used to reduce or eliminate suchdamage. In device 100, protective layer 155 may reduce damage tounderlying organic layers during the fabrication of cathode 160.Preferably, a protective layer has a high carrier mobility for the typeof carrier that it transports (electrons in device 100), such that itdoes not significantly increase the operating voltage of device 100.CuPc, BCP, and various metal phthalocyanines are examples of materialsthat may be used in protective layers. Other materials or combinationsof materials may be used. The thickness of protective layer 155 ispreferably thick enough that there is little or no damage to underlyinglayers due to fabrication processes that occur after organic protectivelayer 160 is deposited, yet not so thick as to significantly increasethe operating voltage of device 100. Protective layer 155 may be dopedto increase its conductivity. For example, a CuPc or BCP protectivelayer 160 may be doped with Li. A more detailed description ofprotective layers may be found in U.S. patent application Ser. No.09/931,948 to Lu et al., which is incorporated by reference in itsentirety.

[0046]FIG. 2 shows an inverted OLED 200. The device includes a substrate210, an cathode 215, an emissive layer 220, a hole transport layer 225,and an anode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

[0047] The simple layered structure illustrated in FIGS. 1 and 2 isprovided by way of non-limiting example, and it is understood thatembodiments of the invention may be used in connection with a widevariety of other structures. The specific materials and structuresdescribed are exemplary in nature, and other materials and structuresmay be used. Functional OLEDs may be achieved by combining the variouslayers described in different ways, or layers may be omitted entirely,based on design, performance, and cost factors. Other layers notspecifically described may also be included. Materials other than thosespecifically described may be used. Although many of the examplesprovided herein describe various layers as comprising a single material,it is understood that combinations of materials, such as a mixture ofhost and dopant, or more generally a mixture, may be used. Also, thelayers may have various sublayers. The names given to the various layersherein are not intended to be strictly limiting. For example, in device200, hole transport layer 225 transports holes and injects holes intoemissive layer 220, and may be described as a hole transport layer or ahole injection layer. In one embodiment, an OLED may be described ashaving an “organic layer” disposed between a cathode and an anode. Thisorganic layer may comprise a single layer, or may further comprisemultiple layers of different organic materials as described, forexample, with respect to FIGS. 1 and 2.

[0048] Structures and materials not specifically described may also beused, such as OLEDs comprised of polymeric materials (PLEDs) such asdisclosed in U.S. Pat. No. 5,247,190, Friend et al., which isincorporated by reference in its entirety. By way of further example,OLEDs having a single organic layer may be used. OLEDs may be stacked,for example as described in U.S. Pat. No. 5,707,745 to Forrest et al,which is incorporated by reference in its entirety. The OLED structuremay deviate from the simple layered structure illustrated in FIGS. 1 and2. For example, the substrate may include an angled reflective surfaceto improve out-coupling, such as a mesa structure as described in U.S.Pat. No. 6,091,195 to Forrest et al., and/or a pit structure asdescribed in U.S. Pat. No. 5,834,893 to Bulovic et al., which areincorporated by reference in their entireties.

[0049] Unless otherwise specified, any of the layers of the variousembodiments may be deposited by any suitable method. For the organiclayers, preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.

[0050] Preferred patterning methods include deposition through a mask,cold welding such as described in U.S. Pat. Nos. 6,294,398 and6,468,819, which are incorporated by reference in their entireties, andpatterning associated with some of the deposition methods such asink-jet and OVJD. Other methods may also be used. The materials to bedeposited may be modified to make them compatible with a particulardeposition method. For example, substituents such as alkyl and arylgroups, branched or unbranched, and preferably containing at least 3carbons, may be used in small molecules to enhance their ability toundergo solution processing. Substituents having 20 carbons or more maybe used, and 3-20 carbons is a preferred range. Materials withasymmetric structures may have better solution processibility than thosehaving symmetric structures, because asymmetric materials may have alower tendency to recrystallize. Dendrimer substituents may be used toenhance the ability of small molecules to undergo solution processing.

[0051] Devices fabricated in accordance with embodiments of theinvention may be incorporated into a wide variety of consumer products,including flat panel displays, computer monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18 degrees C. to 30 degrees C., and more preferably at room temperature(20-25 degrees C.).

[0052] The materials and structures described herein may haveapplications in devices other than OLEDs. For example, otheroptoelectronic devices such as organic solar cells and organicphotodetectors may employ the materials and structures. More generally,organic devices, such as organic transistors, may employ the materialsand structures.

[0053] As used herein, “solution processible” means capable of beingdissolved, dispersed, or transported in and/or deposited from a liquidmedium, either in solution or suspension form.

[0054] The present invention will now be described in detail forspecific preferred embodiments of the invention. These embodiments areintended to be illustrative and the invention is not limited in scope tothe specific preferred embodiments described.

[0055] Industry standards for full color displays call for a saturatedred, green and blue emissive materials. “Saturated blue” means having aCIE coordinate of about 0.155, 0.07. However, a phosphorescent materialmore stable than FIrpic and having a CIE coordinate closer to saturatedblue than FIrpic would be an improvement over presently availablephosphorescent blue emitting materials. “Closer” to saturated blue meanshaving CIE coordinates that are a smaller distance from 0.155, 0.07. Forexample, the distance between FIrpic (CIE 0.17, 0.32) and saturated blueis the square root of((0.17−0.155)²+(0.32−0.07)2), or about 0.25044. So,a stable material having a distance less than about 0.25, and morepreferably less than about 0.125, would be a desirable improvement.Another way to measure the color of emission is by peak wavelength. But,a peak wavelength measurement does not include certain usefulinformation. For example, two different materials may emit spectrahaving the same peak wavelength, yet the emissions may appear differentto the human eye because of the shape of the rest of the emissionspectra. For example, two materials may have a peak wavelength of 470nm. One material may have a sharp peak with very little tail into higherwavelengths, resulting in a saturated blue. The other material may havean extended tail into higher wavelengths, giving it an undesirablegreenish tinge. CIE coordinates account for these differences.

[0056] “Stability” may be measured in a number of ways. One way is anL₁₀₀/L₀ test, which measures the photoluminescent emission of a thinfilm of material over time for at least 100 hours, and provides aparameter indicating what percentage of the original emission is stilloccurring at 100 hours. As used herein, L₁₀₀/L₀ means a stability testperformed at about room temperature, under a vacuum of at least 1×10⁻⁵Torr or in an inert gas, and where the emissive material is incorporatedinto a film similar to one that might be used to make an organic lightemitting device.

[0057] Many phosphorescent blue emitting materials generally haveshortcomings, such as insufficient stability, or insufficient colorsaturation. One blue emitting phosphorescent material is FIrpic, whichhas the structure of Formula 1:

[0058] FIrpic in a non-polar solvent emits a photoluminescent spectrumat CIE 0. 17, 0.32. FIrpic doped at 6% into CBP has an L₁₀₀/L₀ stabilityof 71% at an initial photoluminescent (PL) intensity of about 20 cd/m2.

[0059] In one embodiment of the present invention, a method is providedfor modifying FIrpic and similar materials based on metals other thanIr. The modification may increase stability and/or tune the coloremitted by the material. The substituted molecule has the followingstructure of Formula 2:

[0060] M may be any metal having an atomic weight greater than 40.Preferred metals include Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn,Sb, Te, Au, and Ag. More preferably, the metal is Ir or Pt. Mostpreferably, the metal is Ir.

[0061] R₃ may be any substituent, i.e., R₃ is not H. Preferably, anysubstituent other than CH₃ and F may be used. More preferably, thesubstituent may be selected from the group consisting of alkyl, alkoxy,amino, carboxy, cyano, aryls, and 5 and 6 member heteroaryls. Arylsinclude phenyl and napthyl. Heteroaryls include pyridine, pyrimidine andpyridazine. Any of these substituents may be further substituted. Therelatively low stability of FIrpic is believed to be due in part to thetwo fluorine atoms on the phenyl ring. It has be documented thatfluorine exerts the strongest acidifying effect between all of thehalogens on an aromatic ring and specifically influences the acidifyingeffect at the ortho positions. When the fluorine groups are in a 1,3relationship, hydrogen abstraction occurs in between at the twoposition. See Coe, P. L. et al, J. Chem. Soc. Perkin Trans. 1, 1995 pp.2729-2737 and Bridges, A. J.; J. Org. Chem, 1990, 55 773-775. In themolecule FIrpic the same acidifying effect is observed, that is thehydrogen atom in the 3 position (between the two fluorines illustratedbelow as R₃) can be readily removed leading to instability. Bysubstituting this hydrogen atom with a group that is less easilyremoved, the stability problem may be mitigated.

[0062] In a preferred embodiment, R₃ may be a group in which the atomconnected to the phenyl ring possesses a non-empty p-orbital orn-orbital that may be in π-conjugation or partial π-conjugation with theπ-system in the phenyl ring. It is believed that such an R₃ substituentleads to enhanced stability. One example of such a substituent has acarbon in the R₃ substituent bound to the carbon in the 3 position,where the carbon in the R₃ substituent is bound to at least one otheratom with at least a double bond, or is part of a resonating structuresuch as a phenyl ring. The double bond or resonating structure altersthe orbital structure such that there is π-conjugation or partialπ-conjugation with the π-system in the phenyl ring and the carbon in thesubstituent to which it is bound. Cyano and phenyl substituents provideexamples of such a bonding arrangement. Another example of such asubstituent is one having a lone pair of electrons, such as an oxygenatom or a nitrogen atom.

[0063] R₅ may be H or any substituent. Where a blue-emitting material isdesired, preferred substituents for the R₅ position electron withdrawinggroups. The substituents may be further substituted.

[0064] R′ may be H or any substituent. R′ may represent substitution atany number of sites on the pyridyl ring, including mono-, di-, tri-, andtetra-substitution. Where there is more than one substituent, multiplesubstituents may be linked to each other. Where a blue emitting materialis desired, preferred substituents include electron donating groups.Examples of electron donating groups (when attached to the carbon parato the nitrogen) include methyl, methoxy, amino, dialkylamino, and 5 or6 member cyclic amino groups such as morpholino, pyrrolidino,piperidino. Whether a group is electron donating or electron withdrawingmay depend upon the position to which it is attached.

[0065] The (X—Y) ring in Formula 2 may be referred to as an “ancillaryligand.” (X—Y) may be any mono-anionic ligand. The ligand is referred toas “ancillary” because it is believed that it may modify the photoactiveproperties of the material, as opposed to directly contributing to thephotoactive properties. By way of contrast, the ligand to the left isreferred to as “photoactive” because it is believed that it contributesto the photoactive properties of the material. Although Formula 2illustrates a bidentate ancillary ligand, other structures may be used.The definitions of photoactive and ancillary are intended asnon-limiting theories.

[0066] The subscripts “m” is the number of photoactive ligands of aparticular type, and “n” is the number of ancillary ligands of aparticular type. Depending upon the metal M, a certain number of ligandsmay be attached to the metal. Generally, the ligands are bidentate,which means that they form two bonds with the metal, but bidentateligands are not required. For example, two chlorines could be attachedto the metal in place of a bidentate ancillary ligand. “m” is at leastone, and may be any integer greater than zero up to the maximum numberof ligands that may be attached to the metal. “n” may be zero, and maybe an integer greater than zero, subject to the requirement that “m” isat least one. “m”+“n” may be less than the total number of ligands thatmay be attached to M, such that ligands other than those specificallyillustrated in Formula 2 may also be attached to M. These additionalligands may be photoactive or ancillary. For iridium, to which 3bidentate ligands may be attached, “m” may be 1, 2 or 3, and “n” may be0, 1 or 2.

[0067] The photoactive ligand in Formula 2 has the structure of Formula3:

[0068] Preferred ancillary ligands include acetylacetonate (acac),picolinate (pic) and dipivaloylmetanate (t-butyl acac). Some preferredancillary ligands have the following structure according to Formula 4(pic), Formula 5 (acac), and Formula 6 (t-butyl acac). Other ancillaryligands may be used. Further non-limiting examples of ancillary ligandsmay be found in PCT Application Publication WO 02/15645 A1 to Lamanskyet al. at pages 89-90, which are incorporated herein by reference:

[0069] In a preferred embodiment of Formula 2, n is zero, and m is themaximum number of ligands that may be attached to the metal. Forexample, for Ir, m is three in this preferred embodiment, and thestructure may be referred to as a “tris” structure. The tris structureis preferred because it is believed to be particularly stable. Thestability of the tris structure, combined with the stability and colortuning provided by the R₃ group, may result in a particularly stableblue emitting phosphorescent material.

[0070] In one embodiment of formula 2, m+n is equal to the total numberof bidentate ligands that may be attached to the metal in question—forexample, 3 for Ir. In another embodiment, m+n may be less than themaximum number of bidentate ligands that may be attached to the metal,in which case other ligands—ancillary, photoactive, or otherwise—mayalso be attached to the metal. Preferably, if there are differentphotoactive ligands attached to the metal, each photoactive ligand hasthe structure indicated in Formula 3.

[0071] In addition to enhancing stability, the R₃ substituent group maybe used to tune the color of light emitted by the material. It isbelieved that an R₃ substituent having a negative Hammett value mayred-shift the color emission, while an R₃ substituent having a positiveHammett value may blue-shift the color of emission. The Hammett value ofa group is a measure of whether is withdraws electrons (positive Hammettvalue), or donates electrons (negative Hammett value). The Hammettequation is described in more detail in: Thomas H. Lowry and KathleenSchueller Richardson “Mechanism and Theory In Organic Chemistry,” NewYork, 1987, pages 143-151, which is incorporated by reference. Wherered-shifting is desired, a Hammett value less than −0.18 is preferred.Where blue-shifting is desired, the Hammett value is preferably greaterthan about 0.07, more preferably greater than about 0.2, and mostpreferably greater than about 0.6. These larger Hammett values areparticularly desirable when a blue-emitting phosphorescent material issought. A Hammett value having a smaller absolute value may not have asignificant shifting effect. Where enhanced stability without colorshifting is desired—for example, if a material already emits a desiredspectra, such as saturated green—a Hammett value between about −0.16 and0.5 is preferred. There are circumstances within the scope of thepresent invention where Hammett values outside of the ranges describedmay be appropriate.

[0072] Substituents in the R₅ and R′ positions may also be used to tunethe color emitted by the material. It is believed that thecolor-shifting effect of a substituent having a particular Hammett valuemay vary depending upon where the substituent is attached. For example,it is believed that a substituent attached to any position on the samephenyl ring as R₃ in FIrpic may cause a shift in the samedirection—positive Hammett values correspond to blue shifting, andnegative Hammett values to red shifting. But, a substituent attached toany position on the pyridyl ring may cause a shift in the oppositedirection—positive Hammett values correspond to red shifting, andnegative Hammett values correspond to blue shifting. Notably, the sign(and magnitude) of the Hammett value of a particular substituent maychange depending upon where it is attached. The Hammett valuesassociated with a “para” position, σ para, are used for R₃, because R₃is in the para position to the carbon coordinated to the metal.

[0073] Preferred substituents for the R₃ position include Ph, cyano,4-CF₃Ph, and pyridine. It is believed that each of these substituentsenhance stability. Each of these substituents except Ph also provides ablue shift relative to FIrpic. Ph provides a very mild red-shift, andmay be useful for situations where enhanced stability without asignificant color shift is desired.

[0074] A particularly preferred substituent for the R₃ position is acyano group. It is believed that the cyano group advantageously providesenhanced stability, as well as a significant blue shift of about 15 nmfrom the unsubstituted analog. A substituted material having aphotoactive ligand similar to FIrpic, with a cyano group in the 3position, has the following structure of Formula 7. R₅ and R′ may be Hor a substituent, selected based on considerations similar to thosediscussed with respect to Formula 2.

[0075] Various embodiments of the present invention may be applied to aclass of materials more general than FIrpic derivatives. For example, inone embodiment of the present invention, substitutions may be made tothe following material to enhance stability and/or tune color emission,in accordance with Formula 8:

[0076] R₃ may be selected from the same substituents described withrespect to Formula 2, for similar reasons. Phenyl and cyano groups arepreferred R₃ substituents. CH₃ and F may also be used as a substituentin the R₃ position for materials where the bottom ring is not a 6-memberpyridyl ring. The bottom ring “A” may be a heteroaryl ring system withat least one nitrogen atom that is coordinated to the metal M.Preferably, A is a 5 or 6 member heteroaryl ring system. A single ormultiple additional heteroatoms, such as nitrogen or other heteroatoms,may also be incorporated. The heteroaryl ring may be benzanullated toyield various heteroaryl ring systems, such as quinoline, isoquinoline,and others. The ring may be substituted or unsubstituted in one ormultiple positions. For example, such substituents may include alkyl,halogen, alkoxy, aryl, and/or heteroaryl. R₅ may be selected from thesame substituents described with respect to Formula 2, for similarreasons.

[0077] In one embodiment of the invention, a stable phosphorescentmaterial that emits a saturated blue is sought. In other embodiments,other colors are sought. For example, a saturated green or a saturatedred may be obtained. While green and red phosphorescent materials aregenerally more available in the prior art than blue, embodiments of thepresent invention may lead to phosphorescent materials having bettercolor saturation, better stability, or both.

[0078] Formula 2 is a preferred embodiment of the structure of Formula8.

[0079] As noted above, various embodiments of the present invention maybe applied to a class of materials more general than FIrpic derivatives.For example, an organometallic compound of the present invention can berepresented by the following general Formula 9,

[0080] wherein M is a heavy metal with an atomic weight of greater than40;

[0081] each of R₂ through R₅ and R′₃ through R′₆ are independentlyselected from the group consisting of H, halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, PO₃R, C≡CR, alkyl, alkenyl, aryl, heteroaryl, aryl orheteroaryl groups substituted with halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, orPO₃R, OR, SR, NR₂ (including cyclic-amino), PR₂ (includingcyclic-phosphino), where R is hydrogen, an alkyl group, an aryl group ora heteroaryl group;

[0082] at least one of R₃ and R₅ is either an electron withdrawing groupor an electron donating group;

[0083] m is at least 1,

[0084] n is at least 0; and,

[0085] X—Y may be an ancillary ligand.

[0086] The organometallic compounds of formula 9 comprise a heavytransition metal which produces phosphorescent emission from a mixtureof MLCT and π−π* ligand states. Suitable transition metals include butare not limited to Ir, Pt, Pd, Rh, Re, Os, Tl, Pb, Bi, In, Sn, Sb, Te,Au, and Ag and other heavy metals with an atomic number of at least 40.Preferably an atomic number of at least 72.

[0087] In a preferred embodiment of formula 9, m is an integer from 1 to4, n is an integer from 1 to 3; and

[0088] is a monoanionic non carbon coordinating ligand. In thisembodiment, the metal is bound to at least one mono-anionic, bidentate,carbon-coordination ligand substituted with electron donating and/orelectron withdrawing substituents that shift the emission, relative tothe un-substituted ligand, to either the blue, green or red region ofthe visible spectrum. Further, in this embodiment, the at least onemono-anionic, bidentate, carbon-coordination ligand is substituted withat least one electron withdrawing or electron donating substituent atthe R₃ or R₅ position and the metal is bound to at least one othermonoanionic, preferably, non-carbon coordinating ancillary ligand thatis different than the first mono-anionic, bidentate, carbon coordinationligand. Preferred ancillary ligands are include those described forformula 2.

[0089] In a further preferred embodiment of Formula 9, at least one ofR₃ and R₅ is an electron withdrawing group. The other of R₃ and R₅ isthe same electron withdrawing group, a different electron withdrawinggroup, an electron donating group or hydrogen. In a more preferredembodiment R₃ is an electron withdrawing group and R₅ is the sameelectron withdrawing group, a different electron withdrawing group, orhydrogen.

[0090] In one preferred embodiment of the present invention according toFormula 9, at least one of R₂ and R₄ is an electron withdrawing group.In a more preferred embodiment of the present invention at least one ofR₂ and R₄ is an electron withdrawing group that is not F. In anotherpreferred embodiment R₄ is an electron withdrawing group other than F.

[0091] In a further preferred embodiment R₄ is hydrogen.

[0092] In a preferred embodiment of the present invention according toFormula 9, the electron withdrawing group can be selected from the groupconsisting of halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂,CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or C≡CR, aryl or heteroarylgroups substituted with halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, orPO₃R, where R is hydrogen, an alkyl group, an aryl group or a heteroarylgroup but is not limited to the group listed.

[0093] In a further preferred embodiment of the present inventionaccording to Formula 9, at least one of R₃ and R₅ is an electronwithdrawing group or an electron donating group and R′₄ is an electronwithdrawing group or an electron donating group. In a more preferredembodiment, at least one of R₃ and R₅ is an electron withdrawing groupor an electron donating group and R′₄ is an electron withdrawing groupor an electron donating group such that if neither R₃ nor R₅ is anelectron donating group then R′₄ is an electron donating group and viceversa, if neither R₃ nor R₅ is an electron withdrawing group then R′₄ isan electron withdrawing group.

[0094] Thus, particular preferred embodiments comprise the generalformula 9 where R′₄ is an electron withdrawing group or an electrondonating group such that if neither R₃ nor R₅ is an electron withdrawinggroup then R′₄ is an electron withdrawing group and if neither R₃ nor R₅is an electron donating group then R′₄ is an electron donating group.

[0095] As noted above, the Hammett value of a group is a measure ofwhether is withdraws electrons (positive Hammett value), or donateselectrons (negative Hammett value). As with R₃, the Hammett valuesassociated with a “para” position, σ para, are used for R′₄, because R′₄(like R₃ )is in the para position to the carbon coordinated to themetal. In preferred embodiments, R′₄ is a strong electron withdrawinggroup or a strong electron donating group.

[0096] In a further preferred embodiment of the present inventionaccording to Formula 9, the electron donating group or groups areselected from alkyl, alkenyl, aryl, heteroaryl, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group.

[0097] When electron withdrawing groups are placed in the R₃ position informulas 2 and 9, a hypsochromic (blue) shift in the emission spectrumis observed. The unsubstituted comparative example A (See Table I below)has an emission wavelength of 520 nm. When an electron-withdrawing groupsuch as a trifluoromethyl group is placed in the R₃ position in Formula9, a shift towards higher energy is observed. In combination withanother electron withdrawing group at the R₅ position an additional 40nm hypsochromic shift occurs. The combined additive effect gives ablue/green emission of 470 nm., a blue shift of 50 nm. Other electronwithdrawing groups can be incorporated into these positions to shift theemission wavelength towards higher energies. When a cyano group isincorporated into the R3 position a hypsochromic shift of 20 nm isobserved, giving an emission wavelength of 500 nm. One can tune theemission by incorporating various substituted electron-withdrawinggroups at either the R3 or R5 positions. In addition, one could furthershift the emission wavelength by incorporating electron donating groups,especially on the pyridine ring. When a strong electron donating groupsuch as a dimethylamino group is placed at the R′4 position a furthershift towards a more saturated blue is observed giving an emissionwavelength of 463 nm.

[0098] Conversely, when electron-donating groups are placed at the R₃position a bathochromic (red) shift is observed. The stronger theelectron donating group the greater the bathochromic shift in theemission is observed. Similarly, and in combination with substitutentson the phenyl ring, electron withdrawing groups when placed on thepyridine ring, emission spectra between 500 nm and 650 nm can berealized with the appropriate choice and location of substituents.

[0099] The compounds of the present invention are, in a preferredembodiment, intended for use in a luminescent device. Generally such adevice will comprise an organic layer which comprises the compound ofthe present invention disposed in some manner between two electrodes,one a cathode and the other an anode. The scope of the invention is notto be limited to the theory behind the invention.

[0100] The present invention comprises, in a preferred embodiment, alight emitting device including an emissive layer comprising aorganometallic compound represented by the following general structure,

[0101] wherein M is a metal and at least one of R₃ and R₅ is either anelectron withdrawing group or an electron donating group and wherein mis an integer between 1 and 4 and n is an integer between 1 and 3,; R₄not being F. More specifically, R₄ is an electron withdrawing groupselected from H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂,CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl, alkenyl,aryl, heteroaryl, aryl or heteroaryl groups substituted with halogens,CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R,SO₃R, P(O)R, PO₂R, or PO₃R or an electron donating group selected fromOR, SR, NR₂ (including cyclic-amino), PR₂ (including cyclic-phosphino),where R is hydrogen, an alkyl group, an aryl group or a heteroarylgroup. In preferred embodiments,

[0102] is a monoanionic non carbon coordinating ligand

[0103] In a further preferred embodiment the present invention comprisesa light emitting device including an emissive layer comprising aorganometallic compound represented by the following general structure,

[0104] wherein M is a metal and at least one of R₃ and R₅ is either anelectron withdrawing group or an electron donating group, wherein m isan integer from I to 4 and n is an integer from 1 to 3, and wherein R′₄is an electron withdrawing or an electron donating group such that whenneither R₃ or R₅ is an electron withdrawing group then R′₄ is anelectron withdrawing group and when neither R₃ or R₅ is an electrondonating group then R!₄ is an electron donating group. In a furtherpreferred embodiment,

[0105] is a monoanionic non carbon coordinating ligand

[0106] The present invention comprises, in a preferred embodiment, alight emitting device including an emissive layer comprising aorganometallic compound represented by the following general structure,

[0107] wherein M is a metal and at least one of R₃ and R₅ is selectedfrom the group consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C≡CR, alkyl, alkenyl, aryl, heteroaryl, aryl or heteroaryl groupssubstituted with halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂,CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R and wherein m is aninteger between 1 and 4 and n is an integer between 1 and 3. In afurther preferred embodiment,

[0108] is a monoanionic non carbon coordinating ligand.

[0109] In a preferred embodiment the emissive layer comprises hostmaterial. The host material may comprise an electron transportingmaterial that conducts charge primarily by the transport of electrons.Alternatively the host material may comprise a hole transportingmaterial that conducts charge primarily by the transport of holes. Theorganometallic compound described can be doped in the host material ofthe light emitting device. The organometallic compound has a lowesttriplet excited state with a radiative decay of greater thanapproximately 1×10⁵ per second and the energy level of the lowesttriplet excited state of the host material is higher than the energylevel of the lowest triplet state of the organometallic compound. In apreferred embodiment of the present invention the energy differencebetween the lowest triplet excited state of the organometallic compoundof the present invention and a corresponding relaxed state of theorganometallic compound corresponds with a wavelength of less thanapproximately 520 nm. More preferably the energy difference between thelowest triplet excited state of the organometallic compound of thepresent invention and a corresponding relaxed state of theorganometallic compound corresponds with a wavelength of betweenapproximately 420 nm and approximately 480 nm.

[0110] The organic light emitting devices of the present invention maybe fabricated using methods and materials known in the art.Representative OLED methods, materials and configurations are describedin U.S. Pat. Nos. 5,703,436; 5,707,745, 5,834,893; 5,844,363; 6,097,147;and 6,303,238; each of which is incorporated by reference in itsentirety.

[0111] The compounds described have been represented throughout by theirmonomeric structure. As is well known to those in the art, the compoundsmay also be present as dimers, trimers or dendrimers.

[0112] Aryl alone or in combination includes carbocyclic aromaticsystems or heterocyclic aromatic systems (also known as heteroaryl). Thesystems may contain one, two or three rings wherein each ring may beattached together in a pendent manner or may be fused. Preferably therings have 5 or 6 members.

[0113] Alkoxy includes linear or branched alkoxy groups, preferably C₁to C₆ alkoxy groups, more preferably C₁ to C₃ alkoxy groups.

[0114] Alkyl alone or in combination includes linear or branched alkylgroups, preferably C₁ to C₆ alkyl groups, more preferably C₁ to C₃ alkylgroups.

[0115] Substituted refers to any level of substitution although mono-,di- and tri-substitutions are preferred.

[0116] Material Definitions:

[0117] As used herein, abbreviations refer to materials as follows: CBP:4,4′-N,N-dicarbazole-biphenyl m-MTDATA4,4′,4″-tris(3-methylphenylphenlyamino)triphenylamine Alq₃:8-tris-hydroxyquinoline aluminum Bphen: 4,7-diphenyl-1,10-phenanthrolinen-BPhen: n-doped BPhen (doped with lithium) F₄-TCNQ:tetrafluoro-tetracyano-quinodimethane p-MTDATA: p-doped m-MTDATA (dopedwith F₄-TCNQ) Ir(ppy)₃: tris(2-phenylpyridine)-iridium Ir(ppz)₃:tris(1-phenylpyrazoloto,N,C(2′)iridium(III) BCP:2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline TAZ:3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole CuPc: copperphthalocyanine. ITO: indium tin oxide NPD:N,N′-diphenyl-N—N′-di(1-naphthyl)-benzidine TPD:N,N′-diphenyl-N,N′-di(3-toly)-benzidine BAlq:aluminum(III)bis(2-methyl-8-quinolinato)4-phenyl- phenolate mCP:1,3-N,N-dicarbazole-benzene DCM:4-(dicyanoethylene)-6-(4-dimethylaminostyryl-2- methyl)-4H-pyran DMQA:N,N′-dimethylquinacridone PEDOT:PSS: an aqueous dispersion ofpoly(3,4-ethylenedioxythio- phene) with polystyrenesulfonate (PSS)

[0118] Experimental

[0119] Specific representative embodiments of the invention will now bedescribed, including how such embodiments may be made. It is understoodthat the specific methods, materials, conditions, process parameters,apparatus and the like do not necessarily limit the scope of theinvention.

[0120] In Reaction A shown below, the ligands (III) can be preparedusing the Suzuki method by combining the starting reagents representedby graphic formulae I and II. The substituted or unsubstitutedphenylboronic acids represented by graphic formula I may be purchasedcommercially or prepared using standard techniques as described by thefollowing review; Chem. Rev. 1995, 95, 2457-2483, which summarizes thepalladium catalyzed cross-coupling reactions between organic halides andboronic acids. Compounds represented by graphic formula II, may also bepurchased commercially or prepared by methods described in J. Org. Chem.2002, 67, 238-241. In Reaction A compounds represented by graphicformula I are reacted with the appropriately substituted 2-chloro,bromo,or iodo substituted pyridines represented by graphic formula II and arecombined in an appropriate solvent, e.g. dimethoxyethane (DME), xylenes.In addition, an aqueous base solution e.g., Na₂CO₃, K₂CO₃, K₃PO₄, aPalladium catalyst such as Pd(II) acetate, Pd(PPh₃)₄, and a reducingagent triphenylphosphine (TPP) if necessary is combined and refluxeduntil the reaction is completed. After purification using columnchromatography, moderate to high yields are obtained to give the III asthe final product.

[0121] An alternate route to the desired substituted ligands (III) is touse the Stille reaction shown in Reaction C and described in thefollowing J. Org. Chem. 2002, 67, 238-241 reference.

[0122] Those compounds represented by graphic formula IV can be foundcommercially available while heteroaromatic stannanes represented bygraphic formula V can be prepared using following the methods describedin J. Org. Chem. 2002, 67, 238-241 and depicted in Reaction B.

[0123] In Reaction B, a substituted pyridine is dissolved in a solventunder low temperatures followed by the addition of a base, e.g., butyllithium, followed by the slow addition of the appropreiate electrophile,

[0124] Compounds represented by graphic formulae IV and V shown below inReaction C are combined in a solvent, e.g., xylenes, pyridine, tolueneetc. and reacted in the presence of a Palladium (II) or Palladium (0)catalyst e.g., PdCl₂(PPh₃)₂, Pd(PPh₃)₄ and a reducing agent, PPh₃ ifneeded and reacted to give III. Purification of the crude ligand III isperformed using standard techniques such as column chromatography orprecipitation using common solvents

[0125] In Reaction D, the substituted 2-phenylpyridine ligands preparedfrom Reaction A or Reaction C and represented by graphic formula III,can be reacted with a variety of metals, e.g., iridium, platinum, in thepresence of a solvent, e,g, 2-methoxyethanol or 2-ethoxyethanol andwater under refluxing conditions to produce the dichloro-bridge dimmerrepresented by graphic formula VI. A solid precipitate that is formedupon completion of the reaction is collected by vacuum filtrationtechniques and further purified if necessary.

[0126] In Reaction E the dichlorobridge dimers represented by graphicformula VI can be reacted with a variety of mono-anionic coordinatingligands, e.g. acetonacetyl (acac), picolinic acid,4-dimethylaminopicolinic acid (DMAPic) and mono-anionic metal-carboncoordination ligands e.g., substituted 2-phenylpyridines, etc and isdenoted by X and Y. The final isolated products represented by graphicVII are purified by standard techniques.

Comparative Example A

[0127] 2-Bromopyridine (5.0 g 31.6 mmol), 2,4 difluoroboronic acid (6.0g, 37.9 mmol) and triphenylphosphine (0.83g3.2 mmol) were dissolved in50mL. of dimethoxyethane. To this mixture was added palladium acetate(0.18 g, 0.8 mmol) and 43 mL. of a 2M solution of potassium carbonate.The mixture was heated at reflux for 18 hours. The organic layer wasseparated and the aqueous layer was extracted three times with 125 mL.using ethyl acetate. The organic layers were combined and first washedwith water followed by brine. The organic solvent was dried overmagnesium sulfate, filtered and evaporated to leave an oil. The crudeproduct was purified by column chromatography using silica gel and ethylacetate and hexanes as the eluants. The fractions were collected andcombined to give the desired product 2-(4,6-diflurophenyl)pyridine andwas confirmed by NMR.

[0128] STEP 2: 2-(4,6-Difluorophenyl)pyridine (20.0 g 0.104 mol) fromStep 1 above and iridium chloride hydrate (19.4 g, 0.052 mol) were addedto 300 mL. of 2-ethoxyethanol and heated to reflux for 40 hours. Themixture was then cooled to room temperature, the crudedichlorobidged-dimer was vacuum filtered and washed with 2×150 mL. of2-propanol. The crude dimer was then recrystallized and used in thefollowing step.

[0129] STEP 3: Using a 500 ml flask 10.8 g (8.7 mmol) of the dimmer, 2.1g (17 mmol) of picolinic acid and 9.2 g (87 mmol) were added to 150 mlof 2-ethoxyethanol. This mixture was then heated at reflux for 18 hours.The mixture was then cooled to room temperature and vacuum filtered. Thecollected solid was added to 200 ml of deionized water and stirred atroom temperature for one hour. This mixture was then vacuum filtered andwashed with 100 mL. of ethanol and 100 mL. of hexanes. The collectedproduct was then dried in a vacuum oven. Yield=11.6g. 95.8%.

EXAMPLE 1

[0130] STEP 1: 3,5-Bis(trifluoromethyl)phenylboronic acid (13.5 g, 52mmol), 2-bromopyridine (6.2 g, 39 mmol), palladium (II) acetate (0.29 g,1.3 mmol), triphenylphosphine (1.36 g, 5.2 mmol), and sodium carbonate(7 g, 68 mmol) were added to 200 mL. of 1,2-dimethoxyethane and 100 mL.of water. The reaction mixture was heated to reflux for 5 hours andafter cooling, 100 mL of water and 100 mL. of ethyl acetate were added.The phases were separated, the organic layer was dried over magnesiumsulfate and the excess solvent was removed.2-(3,5-Bistrifluoromethylphenyl)pyridine was purified by columnchromatography and collected as a white solid (7.1 g).

[0131] STEP 2: 2-(3,5-Bis(trifluoromethyl)phenyl)pyridine (1.4 g, 4.8mmol) from Step 1 above and iridium (III) chloride hydrate (0.87 g, 2.4mmol) were added to a flask containing 15 mL. of 2-methoxyethanol and 5mL. of water. The reaction was heated to reflux for 16 hours and allowedto cool. The yellow precipitate that formed was collection by vacuumfiltration. The crude dichloro-bridged dimer was not purified furtherbut used directly as is.

[0132] STEP 3: The dichloro-bridged dimer (0.75 g 0.46 mmol) from Step 2above was added to 50 mL. of 2-methoxyethanol. Sodium carbonate (0.48 g,4.6 mmol) and 2,4-pentanedione (0.46 g, 4.6 mmol) were added to thereaction mixture. The reaction was heated to reflux for 16 hours. Waterwas added and the crude solid was collected through vacuum filtrationand washed with ethanol and hexane. This material was purified by columnchromatography and vacuum sublimation. NMR and Mass Spectroscopy resultsconfirmed the desired compound.

EXAMPLE 3

[0133] STEP 1: 2,4-Difluoro-5-(trifluoromethyl)bromobenzene (2.0 g, 7.7mmol), 2-tributylstannylpyridine, andBis(triphenylphosphine)palladium(II)chloride (0.16 g, 0.23 mmol) wereadded to 50 mL. xylenes and the mixture was heated to reflux for 16hours. The reaction mixture was filtered through a silica gel plug andthen purified with column chromatography to give2-(2,4-difluoro-5-trifluoromethylphenyl)pyridine (1.4 g, 5.4 mmol). Theproduct was confirmed by Mass Spectroscopy and ¹H NMR.

[0134] STEP 2: 2-(2,4-difuoro-5-trifuoromethylpenyl)pyridine (1.4 g, 5.4mmol) and iridium (III) chloride hydrate (0.97 g, 2.7 mmol) were addedto 10 mL. of 2-methoxyethanol and 3 mL. water. The reaction was heatedfor 16 hours and a light green precipitate was collected by vacuumfiltration and washed with ethanol and hexanes. The dichloro-bridgeddimer was dried in a vacuum oven to give 1.0 g (50% yield). The productwas used directly in the next step without further purification.

[0135] STEP 3: The dichloro-bridged dimer (1.0 g, 0.65 mmol), sodiumcarbonate (1.34g, 13.4 mmol), and 2,4 pentanedione (1.3 g, 13.4 mmol)were added to 50 mL. of 2-methoxyethanol and heated to reflux for 16hours. The reaction was cooled and then 50 mL. of water and 50 mL.dichloromethane were added. The phases separated and the organic wascollected. The solvent was removed under vacuum and the product waspurified by column chromatography followed by sublimation. ¹H NMR andMass Spectroscopy results confirmed the desired product.

[0136] Examples 2 and 5-12 were prepared by the Suzuki methods provideby Example 1 Step 1 followed by the synthesis of the dichloride-bridgeddimers and appropriately substituted ancillary ligands.

[0137] Examples 3, 4, 13, 16 and 17 were prepared by the Stille methodsprovided by Example 3 Step 1 followed by the synthesis of thedichloride-bridged dimmer and appropriately substituted ancillaryligands.

[0138] One application for phosphorescent emissive molecules is a fullcolor display. Industry standards for such a display call for pixelsadapted to emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art. CIE coordinates are described in H. Zollinger, “ColorChemistry” VCH Publishers, 1991 and H, J, A, Dartnall, J. K. Bowmaker,and J. D. Mollon, Proc. Roy. Soc. B (London), 1983, 220, 115-130, whichare incorporated by reference. For example, the NTSC standard calls fora saturated blue having CIE (0.155, 0.07). The SRGB standard calls forCIE (0.15,0.06). Other industry standards may call for slightlydifferent CIE coordinates.

[0139] Device fabrication Devices 1, 3, 11, and Comparative Example Awere fabricated by high vacuum (<10⁻⁷ Torr) thermal evaporation. Indiumtin oxide (ITO) anode on glass was used as the anode. The cathodeconsists of 10 Å of LiF followed by 1,000 Å of Al. All devices wereencapsulated with a glass lid sealed with an epoxy resin in a nitrogenglove box (<1 ppm of H₂O and O₂) immediately after fabrication, and amoisture getter was incorporated inside the package. The CIE coordinatesand maximum luminous efficiency (in cd/A) are summarized in followingTable. For the examples without device efficiency, the CIE coordinatesand emission maxima are obtained from the photoluminescence measured inCH₂Cl₂ solution. TABLE 1 OLED max (X) CIE Emission efficiency ExampleDevice M R2 R3 R4 R5 R′4 R′5 R′6 Ligand coordinates (nm) m n (cd/A) A AIr H H H H H H H AcAc (0.33, 0.61) 520 2 1 20 1 1 Ir H CF3 H CF3 H H HAcAc (0.19, 0.39) 472 2 1 17 2 Ir H CF3 H CF3 H H H Pic (0.19, 0.39) 4702 1 3 3 Ir F H F CF3 H H H AcAc (0.17, 0.27) 458 2 1 8.5 4 Ir F H F CF3H H H Pic (0.17, 0.31) 457 2 1 5 Ir H CF3 H CF3 OCH3 H H AcAc (0.17,0.37) 468 2 1 6 Ir H CF3 H CF3 OCH3 H H Pic (0.18, 0.36) 466 2 1 7 Ir HCF3 H H H H H AcAc (0.31, 0.53) 510 2 1 8 Ir H CF3 H H H H H Pic (0.23,0.51) 484 2 1 9 Ir H H H H H H OCH3 Pic (0.34, 0.58) 520 2 1 10 Ir H CF3H CF3 N(CH3)2 H H AcAc (0.18, 0.31) 463 2 1 11 11 Ir H CF3 H CF3pyrrolidon H H AcAc (0.18, 0.29) 462 2 1 2.7 12 Ir H CF3 H CF3pyrrolidon H H DMAPic (0.21, 0.31) 456 2 1 13 Ir F H F CF3 N(CH3)2 H HDMAPic (0.16, 0.22) 450 2 1 14 Ir H CN H H H H H AcAc (0.26, 0.56) 500 21 15 Ir H CN H H H H H Pic (0.22, 0.49) 482 2 1 16 Ir F H H CF3 H H HAcAc (0.19, 0.35) 468 2 1 17 Ir F CN F H H H H Pic 0.15, 0.38 452 2 1 11

Comparative Example A

[0140] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 300 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 ↑ of4,4′-bis(N-carbazolyl)biphenyl (CBP) doped with 6 wt % of Compound A asthe emissive layer (EML), 100 Å ofaluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq), and400 Å of tris(8-hydroxyquinolinato)aluminum (Alq₃).

[0141] Device 1

[0142] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 450 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å ofCompound B doped with 6 wt % of Compound 1 as the emissive layer (EML),and 400 Å of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate(BAlq).

[0143] Device 3

[0144] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 450 Å of4,4′-bis[N-(l-naphthyl)-N-phenylamino]biphenyl (a-NPD), 300 Å ofCompound C doped with 6 wt % of Compound 3 as the emissive layer (EML),and 400 Å of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate(BAlq)

[0145] Device 11

[0146] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 300 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å ofCompound C doped with 6 wt % of Compound 11 as the emissive layer (EML),and 300 Å of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate(BAlq).

[0147] Additional specific substituted FIrpic compounds were synthesizedaccording to the following schemes: In Reaction F shown below, acompound represented by graphic formula X is prepared by combining thestarting reagents represented by formulae VIII and IX. The substitutedor unsubstituted phenylboronic acids represented by graphic formula VIIImay be purchased commercially or prepared using standard techniques asdescribed by the following review; Chem. Rev. 1995, 95, 2457-2483, whichalso summarizes the palladium catalyzed cross-coupling reactions betweenorganic halides and boronic acids. Compounds represented by graphicformula IX, may also be purchased commercially or prepared by methodsdescribed in J. Org. Chem. 2002, 67, 238-241. In Reaction F compoundsrepresented by graphic formula VIII are reacted with the appropriatelysubstituted 2-chloro, bromo, or iodo pyridines represented by graphicformula IX and are combined in an appropriate solvent, e.g.dimethoxyethane (DME), xylenes. In addition, an aqueous base solutione.g., Na₂CO₃, K₂CO₃, K₃PO₄, a palladium catalyst such as Pd(II) acetate,Pd(PPh₃)₄, and a reducing agent triphenylphosphine (TPP) if necessary iscombined and refluxed until the reaction is completed. Afterpurification using column chromatography, moderate to high yields areobtained to give X.

[0148] An alternate route to the desired substituted ligands (X) isshown in Reaction H and described in J. Org. Chem. 2002, 67, 238-241.

[0149] In Reaction H compounds represented by graphic formula XI wherethe X substituent is any halogen that can be prepared or arecommercially available, the heteroaromatic stannanes represented bygraphic formula XII can be prepared using following the methodsdescribed in J. Org. Chem. 2002, 67, 238-241 and depicted in Reaction G(shown below).

[0150] In Reaction G, a substituted pyridine is added to a mixture of.N,N-dimethylethanolamine (DMEA) and butyl lithium at low temperatures.This is followed by the slow addition of the appropriate electrophile,(E+) i.e. tributyl tin chloride, bromine, carbon tetrabromide etc. Thecrude products are purified using standard techniques such as columnchromatography and recrystallization and can be used in Reaction F orReaction H.

[0151] Compounds represented by graphic formulae XI and XII shown belowin Reaction H are combined in a solvent, e.g., xylenes, pyridine,toluene and reacted in the presence of a Palladium (II) or Palladium (0)catalyst e.g., PdCl₂(PPh₃)₂, Pd(PPh₃)₄ and a reducing agent, PPh₃ ifneeded to give the desired ligand represented by graphic formula X.Purification of the crude ligand X is performed using standardtechniques such as column chromatography or precipitation using commonsolvents.

[0152] In Reaction J below, a substituted or unsubstituted ligands aredissolved in anhydrous solvent i.e. THF to which a base i.e. LDA, isadded at low temperatures. After addition of the base, an electrophilei.e, heptafluorobenzyl iodide is added. After the reaction is completethe crude material can be purified by standard conditions such as asilica gel to give the desired product represented by graphic formulaXIII. Compound XIII is then reacted with the appropriate aryl orheteroaryl boronic acid in a similar manner described above in ReactionF to give compound XIV

[0153] Alternatively, in Reaction K shown below, one could preparecompounds represented by graphic formula XIV where R3 is a cyano groupby the following method. A compound represented by graphic formula XVshown in Reaction K below is reacted at low temperatures with anappropriate base such as lithium diisopropyl amide (LDA) and quenchedwith carbon dioxide (CO2). Compound XVI is reacted with thionyl chlorideand ammonium hydroxide to give X as the carboxamide. Compound XVII isthen reacted under dehydrating conditions i.e. acid (H+) to give XVIII.The compound represented by graphic formula XVIII is then converted tothe photoactive ligand by replacing XVIII for XI in Reaction H to giveIII where R3 is now substituted with a cyano substituent.

[0154] In Reaction L, the substituted or unsubstituted photoactiveligands prepared from Reaction J represented by graphic formula XIV, canbe reacted with a variety of metals, e.g., iridium, platinum, in thepresence of a solvent, e.g., 2-methoxyethanol or 2-ethoxyethanol andwater under refluxing conditions to produce the dichloro-bridge dimerrepresented by graphic formula XIX. A solid precipitate that is formedupon completion of the reaction is collected by vacuum filtrationtechniques and further purified if necessary.

[0155] In Reaction M the dichloro-bridge dimers represented by graphicformula XIX can be reacted with a variety of mono-anionic coordinatingligands, e.g. acetonacetyl (acac), picolinic acid,4-dimethylaminopicolinic acid (DMAPic) and is denoted by X and Y. Thefinal isolated products represented by graphic XX are purified bystandard techniques.

[0156] Each of the materials in Table 2 was synthesized. Each materialhad the structure illustrated by Formula 2, where M=Ir, and R₅=R′ ═H.Except for entries 18 and 29, each of the materials had m=2, with oneancillary ligand (n=1) as indicated. Entries 18 and 29 had m=3, asindicated by the “tris” entry in the ancillary column, such that therewas no ancillary ligand. Entries 19 and 21 were synthesized inaccordance with the examples provided above. The other entries weresynthesized using similar techniques apparent to one of skill in the artin view of the examples provided above. A small amount of each materialwas dissolved in dichloromethane. Each solution was optically pumped,and the resultant photoluminescent spectra were measured. The resultantpeak wavelengths and CIE coordinates are tabulated in Table 2. Hammettvalues for the R₃ substituent in the para position (a para) were drawnfrom the literature for compounds 1 σ para for Ph=−0.01), and compounds10 and 11 (σ para for CN=0.66) TABLE 2 Peak OLED ancil- emis- maximumCom- De- lary sion efficiency pound vice R₃ ligand (nm) PL CIE (cd/A) 1831 CO₂Me none 460 0.16, 0.29 14 (tris) 19 19 Ph pic 474 0.17, 0.38 12 204-CF₃Ph pic 470 0.16, 0.33 21 2-pyridine acac 482 0.17, 0.45 222-pyridine pic 468 0.17, 0.34 23 2-pyrimidine acac 484 0.18, 0.46 242-pyrimidine pic 467 0.17, 0.33 25 4-pyridine acac 480 0.15, 0.39 264-pyridine pic 468 0.17, 0.33 27 3-pyridine pic 470 0.17, 0.33 28 28 CNpic 452 0.15, 0.19 11 29 29 CN none 450 0.17, 0.19 7 (tris) 30 30 H pic468 0.17, 0.32 12 (FIrpic)

[0157] Device Fabrication

[0158] Devices 18, 19, 28, 29, and 30 were fabricated by high vacuum(<10⁻⁷ Torr) thermal evaporation. Indium tin oxide (ITO) anode on glasswas used as the anode. The cathode consists of 10 Å of LiF followed by1,000 Å of Al. All devices were encapsulated with a glass lid sealedwith an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂)immediately after fabrication, and a moisture getter was incorporatedinside the package. The CIE coordinates and maximum luminous efficiency(in cd/A) are summarized in Table 2. The CIE coordinates and emissionmaxima are obtained from the photoluminescence measured in CH₂Cl₂solution.

[0159] Device 18

[0160] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 300 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å ofCompound C doped with 6 wt % of Compound 31 as the emissive layer (EML),400 Å aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq).

[0161] Device 19

[0162] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 300 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å of4,4′-bis(N-carbazolyl)biphenyl (CBP) doped with 6 wt % of Compound 19 asthe emissive layer (EML), 400 Å ofaluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq).

[0163] Device 28

[0164] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 450 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å ofcompound C doped with 6 wt % of Compound 28 as the emissive layer (EML),and 400 Å of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate(BAlq).

[0165] Device 29

[0166] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 450 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å ofcompound C doped with 6 wt % of Compound 29 as the emissive layer (EML),and 400 Å of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate(BAlq).

[0167] Device 30

[0168] The organic stack consists of, from the anode to the cathode, 100Å of copper phthalocyanine (CuPc), 300 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD), 300 Å of4,4′-bis(N-carbazolyl)biphenyl (CBP) doped with 6 wt % of Compound 30 asthe emissive layer (EML), 400 Å ofaluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq).

[0169] Compounds 19 and 28 from Table 2, and FIrpic were furthercharacterized for stability. (Compound 28 is identical to compound 17 inTable 1). The photoluminescent stability (PL) testing system used totest these samples monitors PL emission of a sample under UV excitationas a function of time. The system uses a mercury-xenon (Hg-Xe) UV lampto excite a thin film sample on a quartz substrate. The broad UVemission of the lamp is delivered to the sample through a narrow band UVfilter, which selects the 313nm Hg line. During testing, the sample iskept under high vacuum (<5×10⁻⁷ Torr). Silicon diode photodetectorsmonitor the emission intensities of the thin film sample and the lamp.

[0170] Host and dopant were co-evaporated in a vacuum chamber (<5×10⁻⁸Torr) from different sources to form a thin film of 50 nm thickness on aquartz substrate. The dopant was present in a concentration of 6 wt %.The host deposition rate was 1.6 Å/s. Next, the sample was exposed toatmospheric pressure in an inert nitrogen ambient (<1 ppm O₂ and H₂O),where the sample was placed in the PL testing system vacuum chamber andsubsequently evacuated to <1×10⁻⁶ Torr. Next, the sample was exposed to313nm UV radiation at a power density of 0.6 mW/cm2, resulting in a PLintensity of at least 20 cd/m2, and its photoluminescence intensity wasrecorded as a function of time. Also, the UV source intensity wasrecorded as a function of time.

[0171] Three samples were prepared. Sample 1 was Compound 19 doped intoCBP. Sample 2 was compound 28 doped into Compound C. Sample 3 was FIrpicdoped into CBP. The host materials were selected based on energytransfer considerations, and it is not expected that the differences inhost material will significantly affect photoluminescent lifetimetesting results. Each thin film was optically pumped, and thephotoluminescent intensity was measured as a function of time. Theinitial PL intensity was about 20 cd/m2. The results are plotted in FIG.3. Plots 310, 320 and 330 show the photoluminescent intensities of thecompound 19, compound 28, and FIrpic films, respectively. L₁₀₀/L₀values, which indicate the intensity at 100 hours as a percentage of theintensity at zero hours, were also determined for each material. TheL₁₀₀/L₀ values for compound 19, compound 28, and FIrpic were 91%, 82%and 71%, respectively. The plots of FIG. 3, as well as the L₁₀₀/L₀values, demonstrate that compound 19 and compound 28 are more stablethan FIrpic, and demonstrate the more general principal that providing asubstituent in the R3 position increases stability. These results showthat some embodiments of the present invention have emissioncharacteristics similar to FIrpic, or even closer to saturated blue thanFIrpic, and with enhanced stability. Notably, compound 28 has a CIE“distance” of about 0.12 from saturated blue.

[0172] While the present invention is described with respect toparticular examples and preferred embodiments, it is understood that thepresent invention is not limited to these examples and embodiments. Thepresent invention as claimed therefore includes variations from theparticular examples and preferred embodiments described herein, as willbe apparent to one of skill in the art.

1. An emissive material represented by the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through R₅ and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R; OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; m is an integerbetween 1 and 4 and n is an integer between 1 and 3; and,

is a monoanionic non carbon coordinatingcoordinatingcoordinated ligand.2. The composition of claim 1 wherein R₄ is H.
 3. The composition ofclaim 1 wherein at least one of R₃ and R₅ is an electron withdrawinggroup.
 4. The composition of claim 1 wherein R₃ and R₅ are both electronwithdrawing groups.
 5. The composition of claim 1 wherein R₃ is anelectron withdrawing group.
 6. The composition of claim 1 wherein atleast one of R₂ and R₄ is an electron withdrawing group.
 7. Thecomposition of claim 4 wherein at least one of R₂ and R₄ is an electronwithdrawing group.
 8. The composition of claim 1 wherein the electronwithdrawing groups are selected from halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C—CR, aryl or heteroaryl groups substituted with halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, or PO₃where R is a hydrogen, alkyl, aryl or heteroarylgroup.
 9. The composition of claim 1 wherein at least one of R₃ and R₅is an electron donating group.
 10. The composition of claim 1 wherein R₃and R₅ are both electron donating groups.
 11. The composition of claim 1wherein R₃ is an electron donating group.
 12. The composition of claim 1wherein the electron donating groups are selected from alkyl, alkenyl,aryl, heteroaryl, OR, SR, NR₂ (including cyclic-amino), PR₂ (includingcyclic-phosphino), where R is a hydrogen, alkyl, aryl or heteroarylgroup.
 13. The composition of claim 1 wherein the metal is selected fromIr, Pt, Pd, Rh, Re, Os, Ti, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 14. Thecomposition of claim 1 wherein the metal is iridium.
 15. The compositionof claim 1 wherein the metal is platinum.
 16. A composition representedby the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through R₅ and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; m is an integerbetween 1 and 4 and n is an integer between 1 and 3;

is a non carbon coordinated monoanionic non carbon coordinating ligand;and, wherein R′₄ is an electron withdrawing group or an electrondonating group such that if neither R₃ nor R₅ is an electron withdrawinggroup then R′₄ is an electron withdrawing group and if neither R₃ nor R₅is an electron donating group then R′₄ is an electron donating group.17. The composition of claim 16, wherein neither R₃ nor R₅ is anelectron donating group and wherein R′₄ is an electron donating group.18. The composition of claim 16, wherein neither R₃ nor R₅ is anelectron withdrawing group and wherein R′₄ is an electron withdrawinggroup.
 19. The composition of claim 16, wherein at least one of R₃ andR₅ is an electron withdrawing group and R′₄ is an electron donatinggroup.
 20. The composition of claim 16, wherein at least one of R₃ andR₅ is an electron donating group and R′₄ is an electron withdrawinggroup.
 21. The composition of claim 16 wherein the electron withdrawinggroups are selected from halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,or C≡CR, aryl or heteroaryl groups substituted with halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, or where R is a hydrogen, alkyl, aryl or heteroaryl group.22. The composition of claim 16 wherein the electron donating groups areselected from alkyl, alkenyl, aryl, heteroaryl, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is a hydrogen,alkyl, aryl or heteroaryl group.
 23. The composition of claim 16 whereinthe metal is selected from Ir, Pt, Pd, Rh, Re, Os, Tl, Pb, Bi, In, Sn,Sb, Te, Au, and Ag.
 24. A composition represented by the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through Rs and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R; OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; at least one of R₃ andR₅ being selected from the group consisting of CN, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C≡CR, aryl or heteroaryl groups substituted with halogens, CN, CF₃,C_(n)F₂n+₁, trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R,PO₂R, PO₃R, where R is a hydrogen, alkyl, aryl or heteroaryl group,wherein m is an integer between 1 and 4 and n is an integer between 1and 3 and X—Y is non carbon coordinating monoanionic ligand.
 25. Thecomposition of claim 24 wherein at least one of R₃ and R₅ is CN.
 26. Thecomposition of claim 25 wherein at least one of R₂ and R₄ is F.
 27. Thecomposition of claim 26 wherein R′₄ is an electron donating group. 28.The composition of claim 26 wherein R′₄ is NMe₂.
 29. The composition ofclaim 24 wherein at least one of R₃ and R₅ is CF₃
 30. The composition ofclaim 29 wherein at least one of R₂ and R₄ is F.
 31. The composition ofclaim 29 wherein R′₄ is an electron donating group.
 32. The compositionof claim 29 wherein R′₄ is NMe₂.
 33. A light emitting device comprisingan organic layer, the organic layer comprising a composition representedby the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through R₅ and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F₂n+₁, trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; at least one of R₃ andR₅ is either an electron withdrawing group or an electron donatinggroup; m is an integer between 1 and 4 and n is an integer between 1 and3; and,

is a monoanionic non carbon coordinating ligand.
 34. The light emittingdevice of claim 33 wherein at least one of R₃ and R₅ is an electronwithdrawing group.
 35. The light emitting device of claim 33 wherein R₃and R₅ are both electron withdrawing groups.
 36. The light emittingdevice of claim 33 wherein R₃ is an electron withdrawing group.
 37. Thelight emitting device of claim 33 wherein R₂ and R₄ are electronwithdrawing groups.
 38. The light emitting device of claim 33 wherein R₂and R₄ are electron withdrawing groups.
 39. The light emitting device ofclaim 33 wherein at least one of R₃ and R₅ is an electron donatinggroup.
 40. The light emitting device of claim 33 wherein R₃ and R₅ areboth electron donating groups.
 41. The light emitting device of claim 33wherein the electron donating groups are selected from alkyl, alkenyl,aryl, heteroaryl, OR, SR, NR₂ (including cyclic-amino), PR₂ (includingcyclic-phosphino), where R is a hydrogen, alkyl, aryl or heteroarylgroup.
 42. The light emitting device of claim 33 wherein the metal isselected from Ir, Pt, Pd, Rh, Re, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Au,and Ag.
 43. The light emitting device of claim 33 wherein the metal isPt.
 44. The light emitting device of claim 33 wherein the metal is Ir.45. The light emitting device of claim 33 wherein light emitted by theorganic layer has a maximum wavelength of less than 520 nm
 46. The lightemitting device of claim 33 wherein light emitted by the organic layerhas a wavelength of between approximately 420 nm and approximately 480nm.
 47. A light emitting device comprising an organic layer, the organiclayer comprising a composition represented by the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through R₅ and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; at least one of R₃ andR₅ is either an electron withdrawing group or an electron donatinggroup; m is an integer between 1 and 4 and n is an integer between 1 and3;

is a monoanionic non carbon coordinated ligand; and, wherein R′₄ is anelectron withdrawing group or an electron donating group such that ifneither R₃ nor R₅ is an electron withdrawing group then R′₄ is anelectron withdrawing group and if neither R₃ nor R₅ is an electrondonating group then R′₄ is an electron donating group.
 48. The lightemitting device of claim 47, wherein at least one of R₃ and R₅ is anelectron withdrawing group and R′₄ is an electron donating group. 49.The light emitting device of claim 47, wherein R₃ and R₅ are electronwithdrawing groups and R′₄ is an electron donating group.
 50. The lightemitting device of claim 47, wherein at least one of R₃ and R₅ is anelectron donating group and R′₄ is an electron withdrawing group. 51.The light emitting device of claim 47, wherein R₃ and R₅ are electrondonating groups and R′₄ is an electron withdrawing group.
 52. The lightemitting device of claim 47 wherein the electron withdrawing groups areselected from halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂,CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, or C≡CR, aryl orheteroaryl groups substituted with halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, orPO₃R, where R is a hydrogen, alkyl, aryl or heteroaryl group.
 53. Thelight emitting device of claim 47 wherein the electron donating groupsare selected from alkyl, alkenyl, aryl, heteroaryl, OR, SR, NR₂(including cyclic-amino), PR₂ (including cyclic-phosphino), where R is ahydrogen, alkyl, aryl or heteroaryl group.
 54. The light emitting deviceof claim 47 wherein the metal is selected from Ir, Pt, Pd, Rh, Re, Os,Tl, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 55. The light emitting device ofclaim 47 wherein the metal is Pt.
 56. The light emitting device of claim47 wherein the metal is Ir.
 57. The light emitting device of claim 47,wherein light emitted by the organic layer has a maximum wavelength ofless than 520 nm.
 58. The light emitting device of claim 47 whereinlight emitted by the organic layer has a wavelength of betweenapproximately 420 nm and approximately 480 nm.
 59. A light emittingdevice comprising an organic layer, the organic layer comprising acomposition represented by the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through R₅ and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; m is an integerbetween 1 and 4 and n is an integer between 1 and 3; and,

is a monoanionic non carbon coordinating ligand. at least one of R₃ andR₅ is selected from the group consisting of CN, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C≡CR, aryl or heteroaryl groups substituted with halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, PO₃R, where R is a hydrogen, alkyl, aryl or heteroarylgroup.
 60. The light emitting device of claim 59 wherein at least one ofR₃ and R₅ is CN.
 61. The light emitting device of claim 60 wherein atleast one of R₃ and R₅ is CN, and at least one of R₂ and R₄ is F. 62.The light emitting device of claim 60 wherein at least one of R₃ and R₅is CF₃.
 63. The light emitting device of claim 60 wherein at least oneof R₃ and R₅ is CF₃, and at least one of R₂ and R₄ is F.
 64. Acomposition represented by the following structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; R₃ is a substituent having a Hammett value less than about−0.17, between about −0.15 and 0.05, or greater than about 0.07; each ofR₂ through R₅ and R′₃ through R′₆ are independently selected from thegroup consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl,NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R, C≡CR, alkyl,alkenyl, aryl, heteroaryl, aryl or heteroaryl groups substituted withhalogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R,S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R; OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is hydrogen, analkyl group, an aryl group or a heteroaryl group; m is an integerbetween 1 and 4 and n is an integer between 1 and 3; and,

is a monoanionic non carbon coordinating ligand, wherein R₃ and R₅ areselected to provide a hypsochromic shift in the emission spectrum of thecompound of greater than or equal to approximately 40 nm as comparedwith the emission spectrum of a composition with the followingstructure:


65. The emissive material of claim 1 wherein R₃ has a Hammett valuegreater than 0.3
 66. The emissive material of claim 1 wherein R₃ has aHammett value greater than 0.5
 67. The emissive material of claim 1wherein R₃ has a Hammett value greater than 0.6
 68. An emissive materialrepresented by the structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; m is at least 1 n is at least 0 X—Y is an ancillary ligand;R₂ and R₄ are both F; R₃ is a substituent having a Hammett value lessthan about −0.17, between about −0.15 and 0.05, or greater than about0.07; each of R₃, R₅ and R′₃ through R′₆ are independently selected fromthe group consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C≡CR, alkyl, alkenyl, aryl, heteroaryl, aryl or heteroaryl groupssubstituted with halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂,CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R; OR, SR, NR₂(including cyclic-amino), PR₂ (including cyclic-phosphino), where R ishydrogen, an alkyl group, an aryl group or a heteroaryl group
 69. Theemissive material of claim 68 wherein at least one of R₃ and R₅ is anelectron withdrawing group.
 70. The emissive material of claim 68wherein R₃ and R₅ are both electron withdrawing groups.
 71. The emissivematerial of claim 68 wherein R₃ is an electron withdrawing group. 72.The emissive material of claim 68 wherein the electron withdrawinggroups are selected from halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C≡CR, aryl or heteroaryl groups substituted with halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, or PO₃R, where R is a hydrogen, alkyl, aryl or heteroarylgroup.
 73. The emissive material of claim 68 wherein at least one of R₃and R₅ is an electron donating group.
 74. The emissive material of claim68 wherein R₃ and R₅ are both electron donating groups.
 75. The emissivematerial of claim 68 wherein R₃ is an electron donating group.
 76. Theemissive material of claim 68 wherein the electron donating groups areselected from alkyl, alkenyl, aryl, heteroaryl, OR, SR, NR₂ (includingcyclic-amino), PR₂ (including cyclic-phosphino), where R is a hydrogen,alkyl, aryl or heteroaryl group.
 77. The emissive material of claim 68wherein the metal is selected from Ir, Pt, Pd, Rh, Re, Os, Ti, Pb, Bi,In, Sn, Sb, Te, Au, and Ag.
 78. The emissive material of claim 68wherein the metal is iridium.
 79. The emissive material of claim 68wherein the metal is platinum.
 80. The compostion of claim 68 whereinR′₄ is an electron withdrawing group or an electron donating group suchthat if neither R₃ nor R₅ is an electron withdrawing group then R′₄ isan electron withdrawing group and if neither R₃ nor R₅ is an electrondonating group then R′₄ is an electron donating group.
 81. The emissivematerial of claim 80 wherein neither R₃ nor R₅ is an electron donatinggroup and wherein R′₄ is an electron donating group.
 82. The emissivematerial of claim 80 wherein neither R₃ nor R₅ is an electronwithdrawing group and wherein R′₄ is an electron withdrawing group. 83.The emissive material of claim 80 wherein at least one of R₃ and R₅ isan electron withdrawing group and R′₄ is an electron donating group. 84.The emissive material of claim 80 wherein at least one of R₃ and R₅ isan electron donating group and R′₄ is an electron withdrawing group. 85.The emissive material of claim 80 wherein the electron withdrawinggroups are selected from halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,or C≡CR, aryl or heteroaryl groups substituted with halogens, CN, CF₃,C_(n)F_(2n+1), trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R,P(O)R, PO₂R, PO₃R, where R is a hydrogen, alkyl, aryl or heteroarylgroup.
 86. The emissive material of claim 80 wherein the electrondonating groups are selected from alkyl, alkenyl, aryl, heteroaryl, OR,SR, NR₂ (including cyclic-amino), PR₂ (including cyclic-phosphino),where R is a hydrogen, alkyl, aryl or heteroaryl group.
 87. The emissivematerial of claim 80 wherein the metal is selected from Ir, Pt, Pd, Rh,Re, Os, Ti, Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 88. A light emittingdevice comprising an organic layer, the organic layer comprising acomposition represented by the general structure:

wherein M is a heavy metal with an atomic weight of greater than orequal to 40; m is at least 1 n is at least 0 X—Y is an ancillary ligand;R₂ and R₄ are both F; R₃ is a substituent having a Hammett value lessthan about −0.17, between about −0.15 and 0.05, or greater than about0.07; each of R₃, R₅ and R′₃ through R′₆ are independently selected fromthe group consisting of H, halogens, CN, CF₃, C_(n)F_(2n+1),trifluorovinyl, NO₂, CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, PO₃R,C≡CR, alkyl, alkenyl, aryl, heteroaryl, aryl or heteroaryl groupssubstituted with halogens, CN, CF₃, C_(n)F_(2n+1), trifluorovinyl, NO₂,CO₂R, C(O)R, S(O)R, SO₂R, SO₃R, P(O)R, PO₂R, or PO₃R; OR, SR, NR₂(including cyclic-amino), PR₂ (including cyclic-phosphino), where R ishydrogen, an alkyl group, an aryl group or a heteroaryl group
 89. Thelight emitting device of claim 88 wherein at least one of R₃ and R₅ isan electron withdrawing group.
 90. The light emitting device of claim 88wherein R′₄ is an electron withdrawing group or an electron donatinggroup such that if neither R₃ nor R₅ is an electron withdrawing groupthen R′₄ is an electron withdrawing group and if neither R₃ nor R₅ is anelectron donating group then R′₄ is an electron donating group.